Information on Horse Hooves
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As a hoof trimmer, I can tell you that some clients watch the trim closely and are astute in judging what they
observe. Hoof trimmers are happy to hear questions about the horse’s hoof and why some unusual conditions develop. The hoof can be a complex, even a bit mysterious, mechanism, and we appreciate the
opportunity to do some educating. Article for Omega Fields
I’ll touch on two examples here. Both came from clients with a deep interest in their horses’ welfare, and both pertain to conditions that are quite common.
First, let’s discuss the sudden appearance of pinkness near the white line at the bottom of the foot, usually in the toe area. We
come across the condition when picking out and brushing the sole area, or when touching up the bottom edge of the wall with the rasp. It elicits concern, because it correctly implies that it is blood.
It's actually not uncommon to see pink in the white line area after rasping. The pink is there before rasping, of course, but it's
covered with dirt. Rasping cleans things up so we can see details, including color; the pink we see is actually old, well-diluted blood.
Blood vessels abound throughout the entire foot EXCEPT for the wall, which contains no blood vessels at all. The foot
boasts the most concentrated and busiest blood supply in the horse’s entire body (among other benefits, that translates to
heat, which is why the feet of healthy horses don’t freeze). The wall is tightly attached to the foot’s coffin bone by means of
the laminae. Think of the laminae as though it were Velcro, one half of which is attached to the coffin bone, and the other is
the inner “surface” of the wall. The inside half of the laminar connection shares the foot’s rich blood supply, while the outer half contains none.
Interesting – with blood everywhere EXCEPT in the wall, how does it manage get itself down to the bottom of the foot where we see it as a pink stain in the white area?
Let’s briefly get a little technical: the average horse’s hoof wall, about 3/8-inch thick, consists of two substances: vertical,
downward-growing tubules, and holding them in place and providing strength is a material known as intertubular horn. The
tubules are generated from a corium, or source, located in the coronary band, and are very densely packed together at the
outer surface, gradually thinning out a bit as we go deeper into the wall. Intertubular horn cells are generated from the laminae
and grow outward, directly into the clustered tubules, completely drenching them. Thus is formed the structure of densely
packed tubules glued tightly together by intertubular horn -- the extremely tough hoof wall we are all familiar with. Because of
the “thinning out” of the tubules as we look farther into the wall, we conveniently refer to the wall as having two sections –
“outer wall” and “inner wall”. The extreme density of the outer wall makes it an almost impenetrable shield, very effectively
protecting the foot from most outside trauma. The inner wall, lacking the high degree of rigidity provided by the outer wall’s
dense tubule packing, is actually flexible enough to help absorb external shocks that are passed on by the outer wall, thus protecting the more delicate inner foot components.
The point to take home is simply that as the intertubular horn cells move outward through the wall, they are pulled into the
downward flow of tubular growth and migrate to the ground. The rate of descent is generally on the order of about one-half to one centimeter per month.
How does all this explain the pink in the white line? The key is the connection between the two halves of the laminae – the
inner being well supplied with blood, the outer not. The two halves are separated by what amounts to just a thin, waterproof
membrane, and just a nick in that membrane allows some blood to leak out and join the flow of cells that form and replenish
the intertubular horn. That blood is carried downward by the flow of the downward-growing tubules, and voila! -- when that blood contamination reaches ground level, the normally white tissue is suddenly pink.
The ultimate question is, what causes a rupture in the membrane that allows blood leakage into the wall material? There are
several possible causes, the most common being physical trauma – the hoof bumping hard against a rock is a good example.
The resulting membrane tear is tiny and repairs itself quickly, just as do most body wounds, but in the meantime, the wee bit
of blood released through such a break is now in the hoof growth system, and will be borne through it until it reaches the outside world – becoming the pink in the normally white area.
Some measurable time is required for a tiny drop or two of blood to make that journey; since it travels at the same rate as the
growth of the tubules, the pink that appears in the white line area at the bottom of the foot has been in the “system” for what
can be several months. And so, if you see that pink, there is no need for panic.
See what I mean? Complex, somewhat mysterious…
The second example is the problem of the hoof that grows lop-sided and when trimmed for balance always returns to its lop
-sided form. Typically, such a hoof will have the inside wall grow measurably longer than the outside wall, or vice versa.
There are several variations on the theme – most common are toe-in, toe-out, fetlock varus, fetlock valgus, all of which
present as an unbalanced foot. You can painstakingly trim that foot to bring it to a perfect appearance, but before the next scheduled trim date, it will have reverted right back to its unbalanced state.
Unfortunately, trimming such a foot for perfection is an exercise in futility. Most such unbalance cases are caused by an
angular deformity in one or more leg joints, usually slight enough that it isn’t noticed at the joint itself, yet serious enough that it
displaces the other end of a related bone, taking with it all attached components.
The sketch illustrates the concept, using what are called varus and valgus conditions. To explain: note that the line from
shoulder joint to fetlock joint is essentially straight and vertical. Note also that in a leg without serious angular deformity, that
straight line continues through the fetlock and the pastern bones, right to the tip of the toe, as shown in the “ideal leg” example
. When the fetlock joint is deformed so that the pastern bones angle toward the outside the condition is called a fetlock valgus, and when angled toward the inside it’s called a fetlock varus.
You can check your own horses’ fetlock alignments as follows: pick up the leg and balance the cannon bone in your hand.
Wait until the horse relaxes his pastern so it hangs freely. Then mentally draw a line that bisects the cannon bone, hoping that
it continues right on through the pastern and out the toe. That would be essentially an ideal alignment. If the imaginary
bisecting line deviates inward or outward at the fetlock so that it does NOT perfectly bisect the pastern, you’ve got a valgus or varus leg in your hand.
If you have such a deformed fetlock, don’t despair. One, no fetlock is absolutely perfect; two, it’s not hurting your horse; and
three, there’s nothing you can do about it. But you can help by making sure his trim compensates for his deformity. Look at
the hoof representations in the two right-hand examples, compared to the “ideal leg” example. You’ll note that in both valgus
and varus feet, the hoof wall is longer on one side than the other. That’s because the horse always stands and moves in such a
way that he’s as comfortable as possible, and he doesn’t care about how “pretty” his feet grow. The consequence is, one
wall on the foot will receive more wear than the other, eventually resulting in an uneven wear pattern. In addition, the sole of
his foot will, over time, assume an offset angle as well. Unfortunately, the longer wall is often trimmed down to “match” the
shorter wall, with the heel trim adjusted accordingly, until we have a picture-book balanced foot -- but the problem is, to the
horse it feels quite unnatural, maybe even painful; his natural tendency to stand and move always in the most comfortable
manner will cause a return to uneven wall lengths in short order as he wears it back down.
Ironically, you might look at that unbalanced foot and wonder how much it hurts the horse, while the horse is actually quite comfortable and happy with it.
There is no “fix” for this natural unbalance once a horse is fully grown (some measures have been taken with intention to
correct the condition in foals, with mixed results). What you can do is trim the foot so that the horse is most comfortable,
which means leave the long side a tad longer than the short side when you’re done. Natural wear through movement will help
keep it under control, you’ll touch it up again at the next trim, and meantime you’ll have a happy horse.
The same concepts apply to toe-in and toe-out feet. The wear pattern you see on these feet happens because the deformity
moves the functional toe tip toward 1:00 o’clock in one case or 11:00 o’clock in the other just through natural wear.
One condition the trimmer needs to deal with in any of these deformity cases is wall flaring of the long side. It’s necessary to
remove the flares to prevent the foot from developing some serious problems down the line. In addition, the trimmer needs to
pay proper attention to the heel buttresses on a foot with an angular deformity; they will also wear unevenly, and forcing them to balanced appearance will cause the horse discomfort.
Bottom line is the feet (usually the forefeet) of a horse with an angular leg-joint deformity should be trimmed to adapt to the
imbalance and not just to present a pretty picture. They may not end up looking like a cover photo on Hoof Beautiful Magazine, but you’ll have a very happy horse on your hands.
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